Cosmetic products which improve the appearance of skin are increasingly popular with consumers. Frequently, consumers seek to alleviate or delay the signs of aged or photoaged skin, such as fine lines and wrinkles, dry and sagging skin. At the same time, consumers may also seek other benefits in addition to anti-aging, which requires the manufacturer to incorporate several active ingredients into a cosmetic product. Also, cosmetic industry manufacturers continuously strive to improve the efficacy of anti-aging products by combining several anti-aging ingredients.
Unfortunately, it is often difficult to combine various active ingredients, while maintaining their optimum stability. For instance, optimum stability of ascorbic acid is at an acidic pH, yet retinol is particularly unstable at an acidic pH, even though it may be stabilized at a neutral pH. Thus, a product containing ascorbic acid and retinol must keep the actives at two different pH values. While other carboxylic acids, including hydroxy acids, might not have the same stability problem, the acid exists in a formulation only at a lower pH; salts are formed at a higher pH, yet the hydroxy acids are most effective at an acidic pH. Again, the need exists to maintain hydroxy acids and retinol at two different pHs. Currently, the incompatible actives (i.e., actives which require different pH environments for stability or chemical activity) are protected by separating them in double barrel chambers. Another conceivable separation method is to sequester the actives in different phases of a multiple emulsion (e.g., oil-in-water-in-oil or water-in-oil-in-water). Double barrel chambers, however, are too costly for mass market applications and multiple emulsions are known to be very fragile (see Fox, Cosmetics and Toiletry, vol. 101, November 1986, p 101-112).
Canadian Patent Application 2,162,821 (Colgate-Palmolive) discloses a multilayer bicarbonate/peroxide dentifrice. Bicarbonate and peroxide are maintained in stable discrete layers. The composition of the two layers is very different from the cosmetic emulsions employed in the present invention. Indeed, in the '821 application the two layers are essentially anhydrous systems. Furthermore, the '821 application does not mention any pH values and does not employ emulsions with different pH values.